Mobile communication devices are evolving towards small platforms that incorporate multiple radio interfaces. For example, a smartphone or other hand-held device may include a cellular transceiver (e.g., GSM/WCDMA/LTE) to communicate with a base station in a wireless communication network, a wireless local area network (WLAN) transceiver (e.g., WiFi) for communicating with access nodes in local area network (LAN), and a Bluetooth transceiver for communicating with other nearby devices. Each radio transceiver requires one or more antennas. Given the inherent space limitations, it is difficult to provide complete isolation between the antennas for the different radio interfaces. Therefore the coexistence of different radio interfaces in a single device poses new design challenges.
One problem is that the cellular transmitter can desensitize the WLAN receiver and Bluetooth receiver when operating at high transmit power levels. The desensitization of the WLAN and Bluetooth receivers can be in the range of 20-30 dB, severely degrading the link quality and throughput of these systems. Such desensitization depends to some extent on the efficiency of the filters (e.g., surface acoustic wave (SAW) or bulk acoustic wave/film bulk acoustic resonator (BAW/FBAR)) in the cellular transmitter and WLAN/Bluetooth receiver chains, but also to a large extent on the isolation between the antennas used. Because the antenna performance and isolation can vary widely due to normal activities of the user, it is difficult to design devices that provide the necessary isolation between antennas in all circumstances.
One way to avoid desensitization is to limit usage of the WLAN and Bluetooth interfaces to times when the cellular transmitter is not operating. However, it is desirable from a consumer perspective to enable simultaneous use of the WLAN and Bluetooth receivers with the cellular transmitter.